Fix rubocop violation in gemspec

Author: ukdave

semantic_release.gemspec

@@ -24,7 +24,6 @@ Gem::Specification.new do |spec|
 
   # Specify which files should be added to the gem when it is released.
   # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
-  gemspec = File.basename(__FILE__)
   spec.files = IO.popen(%w[git ls-files -z], chdir: __dir__, err: IO::NULL) do |ls|
     ls.readlines("\x0", chomp: true).select do |f|
       f.start_with?(*%w[CHANGELOG.md LICENSE.txt README.md lib])